Abstract

Spatial distribution patterns of arsenic (As) in the tissues of a lesser-known As hyperaccumulating fern Pityrogramma calomelanos (L.) Link var. austroamericana (Domin) Farw. (Pteridaceae) have been studied. Quantitative micro-proton-induced X-ray emission (micro-PIXE) spectroscopy was employed to examine As localization in pinnule and stipe cross-sections of this species. In addition, As hyperaccumulation status of P. calomelanos var. austroamericana was compared with the well-known As hyperaccumulating fern Pteris vittata L. Both species were grown in pots under controlled conditions and exposed to four levels of As (0–500 mg As kg−1) for 20 weeks. Pityrogramma calomelanos var. austroamericana accumulated up to 16 415 mg As kg−1 dry weight (DW), however, phytotoxicity symptoms such as necrotic pinnule tips and margins, appeared in fronds with concentrations >3,008 mg As kg−1 DW. Arsenic was readily translocated to fronds, with concentrations up to 75 times greater in fronds than in roots. Quantitative elemental maps of As generated using micro-PIXE analysis revealed that As concentrations in pinnule cross-sections were higher than in stipe cross-sections with concentrations of 3.7 × 103 and 1.6 × 103 mg As kg−1 DW, respectively (as determined by region selection analysis; RSA). In pinnules, RSA revealed variable concentrations of As, however did not resolve a clear pattern of compartmentalization across different anatomical regions. In stipe tissues, As concentrations followed the order vascular bundle > cortex > epidermis (as determined by RSA). Our results show that P. calomelanos var. austroamericana is an As hyperaccumulator and has the potential for use in phytoremediation of soils with low levels (up to 50 mg kg−1) of As contamination.

Notes

Acknowledgements

We acknowledge the Australian Institute of Nuclear Science and Engineering for financial assistance (AWARD no. AINGRA 06160) and the financial assistance provided by the Australian Government through an Australian Postgraduate Award scholarship to the first author. The authors would like to thank Nanjappa Ashwath for assistance with field collection of plant material, Carol Campbell for assistance with anatomical interpretations and George and Valerie Sonter for supplying P. vittata. We thank the two anonymous reviewers for their constructive comments on an earlier version of this manuscript.